The long range goal is to provide the knowledge base for the design of methods for inducing chronic, controlled swelling of red cells in individuals homozygous for Hb S. The low cation permeability of red cells relative to other tissues makes it feasible to propose pharmacologic methods for inducing red cell swelling. However, before such strategies can be designed, it will be necessary to understand how the SS red cell would respond to attempts to increase its volume. Also, an animal model of human SS red cell volume regulation would be very useful in developing approaches to the problem of in vivo cell volume manipulation. There is evidence that osmotic swelling of human SS red cells causes the activation of a C1-dependent K transport system that is very similar to one that we have recently observed in rabbit red cells. This K efflux system is probably responsible for cell volume regulation, and it will be essential to understand this system in order to optimize strategies for swelling the cells. The first aim is to compare the characteristics of K efflux (using 86Rb as tracer) in oxygenated human SS and rabbit red cells, in order to evaluate the rabbit as an animal model. Another aim is to find irreversibly acting inhibitors of the swelling-stimulated K efflux; such inhibitors will allow us to determine whether the system is really essential for cell volume regulation. Irreversible inhibitors of the K efflux could also lead to extracorporeal treatments that would cause red cell swelling. In order to identify the transport protein that catalyzes the swelling-stimulated K efflux, we will raise monoclonal antibodies, using a screening procedure to select antibodies that inhibit the K efflux. Such antibodies would be very valuable in future molecular-level work on the transport system. The last major aim of the proposal is to begin to characterize the regulation of cation transport in the maturing reticulocyte. Very significant changes in cation transport take place during reticulocyte maturation, and an understanding of these changes will be essential in the design of strategies for long-term manipulation of red cell volume.